Add support to write Json file

Fixes #129

src/Cake.Markdownlint.Tests/NodeJs/MarkdownlintNodeJsRunnerTests.cs

@@ -54,6 +54,18 @@ public void OutputFile_Should_Be_Added_If_Settings_Are_Passed()
 
                 result.Args.ShouldBe("-o \"c:/foo.log\" \"c:/directory-to-lint\"");
             }
+
+            [Fact]
+            public void JsonFormatArgument_Should_Be_Added_If_Settings_Are_Passed()
+            {
+                var fixture = new MarkdownlintNodeJsRunnerFixture();
+                fixture.Settings.OutputFile = @"c:\foo.log";
+                fixture.Settings.JsonFormat = true;
+
+                var result = fixture.Run();
+
+                result.Args.ShouldBe("-o \"c:/foo.log\" \"c:/directory-to-lint\" -j");
+            }
         }
     }
 }

src/Cake.Markdownlint/NodeJs/MarkdownlintNodeJsRunnerSettings.cs

@@ -41,6 +41,11 @@ protected MarkdownlintNodeJsRunnerSettings(DirectoryPath directory)
         /// </summary>
         public FilePath OutputFile { get; set; }
 
+        /// <summary>
+        /// Gets or sets the value if the log file will be written in json format or not.
+        /// </summary>
+        public bool JsonFormat { get; set; }
+
         /// <summary>
         /// Gets or sets a value indicating whether an exception should be thrown if an issues was
         /// detected.
@@ -92,6 +97,11 @@ internal void Evaluate(ProcessArgumentBuilder args)
             {
                 args.AppendQuoted(this.directory.FullPath);
             }
+
+            if (this.JsonFormat)
+            {
+                args.Append("-j");
+            }
         }
     }
 }